Convert Calories to Joules

The Calorie (symbol: cal) is a unit of energy. The 'small' gram-calorie (also called thermochemical calorie), defined as exactly 4.184 joules per ISO 31-4 / IUPAC convention — the energy needed to raise one gram of liquid water by 1 °C at standard conditions. This is the scientific calorie used throughout chemistry, physics, and biochemistry literature: enzyme kinetic data, calorimetric measurements (DSC instruments report energy in cal/g for melting transitions), Hess's law calculations, and the thermochemistry tables in the CRC Handbook all use cal. The gram-calorie is NOT the larger 'Calorie' (Cal, capital C) used on US food labels, which is actually a kilocalorie (1 Cal = 1 kcal = 1,000 gram-calories). The cal/Cal naming clash is a notorious source of confusion when cross-referencing nutrition data against scientific literature — a 'low-calorie' food labelled 'only 100 Calories' delivers 100,000 small calories. Two slightly-different historical 'calorie' definitions exist (thermochemical 4.184 J; 'International Table' or IT calorie 4.1868 J), with the thermochemical version dominant in modern usage.

Calories are commonly used in nutrition, electrical billing, physics, and mechanical engineering.

The Joule (symbol: J) is a unit of energy. The SI unit of energy, work, and heat (ISO 80000-5 §5-20), equal to exactly one newton-meter — the energy transferred when a force of one newton acts over a distance of one meter (1 J = 1 N·m = 1 kg·m²/s²). Named for physicist James Prescott Joule, whose 1843-1845 paddle-wheel experiments established the mechanical equivalent of heat (4.184 J ≡ 1 cal) and laid the foundation for the First Law of Thermodynamics. The joule is the universal reference for energy in physics, engineering, chemistry, and biology. Reference scale: a falling apple releases ~1 J; a food Calorie (kcal) is 4,184 J; a AA battery stores ~10,000-15,000 J; a slice of pizza is ~1.2 MJ (300 kcal); a gallon of gasoline ~120 MJ (33 kWh); a US household's daily electricity ~80-100 MJ. Convert J to kWh by dividing by 3,600,000; to calories by dividing by 4.184; to BTU by dividing by 1,055.06; to eV by dividing by 1.602 × 10⁻¹⁹.

It belongs to the metric measurement system.

Joules are commonly used in nutrition, electrical billing, physics, and mechanical engineering.